add riak_test for legacy s3 rewrite module.
add riak_test for legacy s3 rewrite module.

sdebnath/riak_cs,GabrielNicolasAvellaneda/riak_cs,dragonfax/riak_cs,basho/riak_cs,yangchengjian/riak_cs,GabrielNicolasAvellaneda/riak_cs,sdebnath/riak_cs,yangchengjian/riak_cs,laurenrother/riak_cs,sdebnath/riak_cs,basho/riak_cs,yangchengjian/riak_cs,basho/riak_cs,basho/riak_cs,GabrielNicolasAvellaneda/riak_cs,dragonfax/riak_cs,laurenrother/riak_cs,sdebnath/riak_cs,laurenrother/riak_cs,dragonfax/riak_cs,laurenrother/riak_cs,dragonfax/riak_cs,GabrielNicolasAvellaneda/riak_cs,yangchengjian/riak_cs